This invention relates to a sliding roof seam construction to accommodate differential expansion of adjacent metal panels.
A typical metal roof construction includes an array of metal purlins laid across structural beams. The purlins and beams are referred to below as the “substructure” of the roof. Most purlins have a “C” or “Z” cross-section with upper and lower flanges at either edge of a central web. “Z”-shaped members are popular because they have the advantage of being nestable. The roof substructure supports an array of interlocked metal roof panels, often with a layer of insulation beneath the panels. The roof panels are laid perpendicularly across the purlins so that, on a ridge roof, the panels extend from the ridge to the eave. Normally, the panels are fixed to the eave, and are supported in a way that lets them expand and contract lengthwise, yet prevents them from being lifted off the purlins by high winds. Widthwise expansion is not normally a problem, because the panels are typically corrugated; however, lengthwise expansion cycles can be considerable, inasmuch as ambient temperatures vary annually by as much as 100° F. The upper extreme is augmented by solar heating, which causes the to roof expand and contract considerably, even at constant ambient temperature, as the sun rises, sets and is hidden by clouds. For these reasons, roof panels must be connected to the substructure in a way that permits the panels to move considerably in the lengthwise direction. Usually the panels are fixed to the substructure at the eaves, and are permitted to expand toward the roof ridge, where their ends are covered loosely by a cap.
In a standard warehouse-style building with a rectangular footprint, the panels are all the same length, and as the panels are laid, their overlapped edges are tightly folded over to form a weather-proof structure. Various specialized roof seaming machines exist for this purpose. Panels of equal length expand and contract in unison as thermal variations occur.
When a roof has an inside corner, however, panels of one length are laid adjacent panels of a substantially different length, extending from eaves at different distances from the ridge. Such a roof is illustrated in FIG. 4. When the panels are heated or cooled, differential thermal expansion causes relative lengthwise movement in the panels on either side of the “shear line” SL. The edges of these panels cannot be seamed together without creating a danger of buckling or other structural damage resulting from differential thermal expansion.